int interface_login(char * username, char * passwd, int level, int flag);
int interface_add_user(char * username, char * passwd);
int interface_delete_user(char * username);
int interface_add_file(char * filename, char * content);
int interface_delete_file(char * filename);
int interface_revoke_right(char * username, char * filename, char * right);
int interface_transfer_right(char * username, char * filename, char * right);
const char * interface_get_current_user(char * username);
int interface_test();
int interface_get_subjects_num();
const char * interface_get_subjects_name(int i);
const char * interface_get_subjects_passwd(int i);